1. Technical Field
The present invention relates generally to a testing system for use in programming an implantable cardioverter defibrillator prior to implantation. More hardware and software designed to eliminate repeated arrhythmia induction by the real-time capture and storage of an electrogram which can be replayed into ICD software simulators to determine ICD programming parameters.
2. Summary of Related Art
The pumping action of the heart is effected by the spontaneous generation of an electrical impulse or action potential. The electrical impulse is conducted throughout the heart, causing subsequent contraction of the myocardium in response. The origin of the heart's electrical impulse is the sino-atrial node. The impulse is conducted to all portions of the atria through cell-to-cell transmission, whereby contraction of the atrial chambers results. Once initiated, the impulse continues to the atrioventricular node (or "A-V node"), which is a cluster of conduction fibrils. The A-V node functions as a delaying mechanism or a buffer to slow conductio of the received electrical impulse by about one-tenth of a second. This brief delay of transmission of electrical impulse from the atria to the ventricles allows for proper blood flow between the chambers.
The A-V node thereafter transmits an electrical impulse to the bundle of His. This bundle comprises the left and right bundle branches of the His-Purkinjie system. Purkinjie fibers are located at the terminal ends of the bundle branches, forming the electrical link to the myocardial cells themselves.
The conducted electrical impulses define a coordinated wave of electrical activity which effect simultaneous contraction of plural myocardial cells. The impulses initially cause depolarization, and sequential contraction of cardiac muscle of the atria and ventricles follows.
While the electrical system of the heart operates with astonishing regularity in most people, proper functioning is impaired when the heart experiences aberrations in electrical origination or transmission. When electrical failure or a change from normal electrical transmission occurs, the result is a change in sequence of cardiac activity or an arrhythmia. An arrhythmia may be atrial, atrioventricular, or ventricular. Ventricular tachycardia and ventricular fibrillation are of greatest concern and may be lethal. During an episode of ventricular tachycardia, the sequence of ventricular extrasystoles occurs at a rate of between 110 and 240 cycles per minute. If sustained, ventricular tachycardia may eventually lead to ventricular fibrillation in which the ventricular extrasystoles reach a frequency in excess of 330 cycles per minute. It is the sustained ventricular tachycardia which may lead to death if not resolved within minutes.
There are a variety of approaches to the treatment of arrhythmia. Approaches include drug therapy, radio frequency ablation, and the implantable cardioverter defibrillator.
Calcium antagonists are the drugs of choice for treatment. These drugs regulate electrical conduction by blocking the calcium channels of myocardial cells.
Radio frequency ablation includes the placement of a catheter into the heart. High frequency radio waves are then introduced into the heart through the catheter to remove the faulty area through burning to neutralize faulty accessory electrically-conductive pathways.
One of the most common methods for treating arrhythmia is through electrical therapy delivered directed to the heart or through the body to the heart. Electrical currents or shocks are delivered to the heart to alter its rhythm. An implantable cardioverter defibrillator or ICD has electrodes which are connected to the heart.
The modern ICD is a small, battery powered device which stimulates the heart directly using function generators having specific waveforms to respond to and treat arrhythmias. The ICD and its electrode leads are implanted in the patient. The ICD monitors the activity of the heart and, when a determination is made that an irregularity such as ventricular fibrillation is occurring, the ICD delivers a relatively large defibrillation countershock to the electrodes implanted about the heart to return the heart to a prescribed heart rhythm rate. The defibrillation electrical countershock is typically in the range of between 25 and 40 joules. The countershock is relatively significant and is generated by high voltage capacitors which may be charged to between about 650 and 750 volts.
Installation of the ICD and its accompanying electrodes includes more than surgical insertion and attachment. Almost all known implantable ICD's may be configured or programmed to customize the functioning of the ICD to the particular needs of the patient. Each programmable ICD includes a set of parameters to respond to the needs of the individual patient in the most optimum way. Such parameters include fibrillation detection rate, high rate tachycardia detection rate, and rate cutoff for low rate ventricular tachycardia. The accuracy of the parameter settings for applying appropriate therapy are critical. For example, if the rate setting for defibrillation or cardioversion detection is too high, a fibrillating heart may be overlooked. If the setting for defibrillation or cardioversion detection is set too low, the ICD will incorrectly deliver an unnecessary countershock.
While automization of the programming of the ICD has been proposed (for example, the Sensolog [trademark; Siemens-Elema AB] pacemaker is alleged to be autoprogrammable), the typical ICD requires manual programming. Programmable pacemakers include, for example, the Activitrax II Models 8412-14 [trademark; Medtronic Inc.], the Legend Models 8416-18 [trademark; Medtronic Inc.], the Meta MV Model 1202 [trademark; Telectronics], the Sensor Model Kelvin 500 [trademark; Cook Pacemaker Corporation], the Prism CL Model 450A [trademark; Cordis Pacing System], and the Nova MR [trademark; Intermedics]. Each of these units requires at least some manual physician programming for parameters such as mode, sensitivity, threshold lower and upper rates, pulse amplitude, refractory period and pulse width.
While programmable features as well as procedures for programming the various pacemakers vary from one manufacturer to the next, each of the programmable ICD's requires that the programmer establish one or more baselines to provide the values necessary for programming the particular pacemaker to the particular needs of the afflicted individual. One method of obtaining a baseline is to have the patient undertake a certain minimum level of physical activity. However, the only accurate way to provide the necessary values to respond to the particular patient's arrhythmia is to induce the arrhythmia itself. Given in a controlled environment, this is of minimum risk to the patient. However, repetitious induction of the arrhythmia is usually required and, regardless of the safety of the environment, repeated inductions is not the preferred resolution.
Recognizing the shortcomings of known technologies, several approaches have been proposed in an effort to overcome difficulties in programming the ICD prior to implantation. Examples include: U.S. Pat. No. 5,226,413, issued Jul. 13, 1993, to Bennet et al. for "Rate Responsive Pacemaker And Method For Automatically Initializing The Same," which teaches a pacemaker system that includes a dual sensor implantable pacemaker and an external programmer for automatically and simultaneously optimizing and initializing a plurality of pacing parameters; U.S. Pat. No. 5,292,341, issued on Mar. 8, 1994, to Snell for "Method And System For Determining And Automatically Adjusting The Sensor Parameters Of A Rate-Responsive Pacemaker," which teaches a rate-responsive pacing system and method that allows the inter-related sensor operating parameters associated with the physiological sensor of a rate-responsive pacemaker to be automatically and/or optimally set for a particular patient; U.S. Pat. No. 5,421,830, issued Jun. 6, 1995, for Epstein et al. which teaches a programming system that allows a physician or medical personnel to optimize the settings of various arrhythmia detection criteria and/or parameters related to hemodynamic performance to be programmed into the implanted cardiac stimulating device; and U.S. Pat. No. 5,607,460, issued Mar. 4, 1997, to Kroll et al. for "Physician Interface Expert System For Programming Implantable Arrhythmia Treatment Devices," which teaches an interface expert system that allows a physician not well versed in ICD parameters to program at least one parameter into an ICD using the physician's existing knowledge of the patients medical history.
While each of these references provides a contribution to the art of the programming of parameters for pacemakers, a simple yet exacting method of programming remains wanting.